Austentic alloy steels



Patented Sept. 7, 1948 TITOFFICE Aus'rnm'rro ALLor STEEL'S Alfred Everett Thornton, Sheflield, England, assignor to Thos'. Firth & John Brown Limited, Sheffield, England, a British company No Drawing. Application July 2,

1946, Serial No.

r 681,135. In Great Britain July9, 1945 8 Claims. (01. 148 31 This invention comprises improvements in or relating to alloy steels and more particularly to high expansion austenitic steels suitable for use in the manufacture of internal-combustion engines and containing at least 0.35% of carbon, from 3.5% to 6% manganese and from 3.0% to 7.0% chromium, together with a proportionof nickel and asmall quantity of a stabilising-element such as vanadium, tungsten, titanium or columbium.

Known alloy steels of this character, which normally contain from 11% to 16% nickel and not more than 0.9% carbon, require heat treatment at a low temperature of the order of 700 C. to obtain optimum physical properties and it is known that the heat-treated material is difficult to machine.

We have found that the machining difliculties are reduced to a marked extent by the addition to the alloy of a proportion of copper, either with nickel in the proportion of 11% to 16% or with a reduced proportion of nickel. The alloy steel according to our invention, therefore, comprises a minimum carbon content of 0.35%, from 3.5% to 6% of manganese and from 3% to 7% of chromium together with a proportion of nickel and copper and a small addition of one or more stabilising elements such as vanadium, tungsten, titanium or columbium.

The proportion of nickel may be from 11% to 16% together with copper from 0.5% up to a maximum of 12%. Alternatively the proportion of nickel may be reduced and additional copper added in place of the nickel in equivalent proportions but the remaining nickel content should be greater than the additional copper used over 12%.

The alloy according to the invention is heattreated at a low temperature, usually 700 C.- 750 C. to give it the optimum tensile properties and the heat-treated metal is more easily processed in essential machining operations such as turning, shaping, milling, drilling, tapping and grinding than in similar alloys containing no copper. Owing to the easier machinability of the metal, the degree of internal stresses set up in the metal during the machining operations are materially reduced with consequent reduction in the distortion of the machined components.

The improved steel has the further advantage that it can be readily nitrided.

It is further found that the addition of copper to alloy steels of this character improves the resistance of the metal to fatigue, for exampleQthe addition of 2% copper, to an alloy con taining carbon 0.49%, silicon 0.72%, manganese 5.01%, chromium5.5%, nickel 13.5%, vanadium 0.32% increases the fatigue limit of the material vto :21.5 tons perv square inch from :17.0 tons per square inch. Such an alloy with a 2% copper addition istypical of the invention. The

proportions of the constituents may, however, be varied Within the limits hereinbefore indicated and tungsten, titanium, columbium or other stabilising elements may be used in the place of the vanadium.

I claim:

1. A high expansion austenitic steel suitable for use in the manufacture of internal-combustion engines and containing carbon between 0.35% and the usual upper limits of carbon in austenitic steels, manganese from 3.5 to 6%, chromium from 3 to 7%, nickel from 9 to 16%, copper from 0.5 to 12%, silicon 0 to 2.0%, a small proportion of a carbide forming element taken from the group consisting of vanadium, tungsten, titanium and columbium, the remainder being substantially all iron and the steel having been normalized at a minimum of 700 C. to obtain optimum physical properties.

2. A high expansion austenitic steel suitable for used in the manufacture of internal-combustion engines and containing carbon between 0.35% and 0.90%, manganese from 3.5 to 6%, chromium from 3 to 7%, nickel from 9 to 16%, copper from 0.5 to 12%, silicon 0 to 2.0%, a small proportion of a carbide forming element taken from the group consisting of vanadium, tungsten, titanium and columbium, the remainder being substantially all iron and the steel having been normalized at a minimum of 700 C. to obtain optimum tensile properties.

3. A high expansion austenitic steel suitable for use in the manufacture of internal-combustion engines and containing carbon between 0.35% and 0.49%, manganese from 3.5% to 6%, chromium from 3 to 7%, nickel from 9 to 16%, copper from 0.5 to 12 silicon 0 to 2.0%, a small proportion of a carbide forming element taken from the group consisting of vanadium, tungsten, titanium and columbium, the remainder being substantially all iron and the steel having been normalized at a minimum of 700 C. to obtain optimum physical properties.

4. A high expansion austenitic steel suitable for use in the manufacture of internal-combustion engines and containing carbon between 0.35% and 0.9%, manganese from 3.5 to chromium from 3 to 7%, nickel from 11 to 16 copper from 0.5 to 12%, silicon 0.2 to 2.0% and a small proportion of a carbide forming element taken from the group consisting of vanadium, tungsten, titanium and columbium, the remainder being substantially all iron and the steel having been normalized. at a minimum of 700? C. to obtain optimum physical properties.

5. An austenitic alloy steel comprising copper 2%, carbon 0.49%, 5.01%, chromium 5.5%, nickel 13.5%, vanadium 0.32%, the remainder being iron and; the; steel having been normalized at a minimuml 0117,00" C. to obtain optimum physicalpmperties;

6. A normalized austenitic alloy steelghaving a fatigue limit of approximately 12125 tons per square inch and consisting of copper-2%., car-l bon 0.49%, silicon 0.72%, manganese 5.01%, chromium 5.5%, nickel 13.5%, vanadium 0.32%.; and iron the remainder.;

I.,A.high expansion austenitic steel suitable. for usein thelmanuiacture of internal-combustion, engines; and containing carbon between 0.35% and,v the usualupper limits of carbon in austenitic steels, manganese from 3;5;-to 6%, chromium from 3 to '7;%, nickel from 9 to 16%, copper from 0:5 to 12 silicon 0- to 2.0 a-small proportion of a carbideiorming element taken from the'group consistingyof vanadium, tungsten, titanium and: columbium,; the ,remainder; be-

silicon 0.72%, manganese taken, from; th r p ing substantially all iron been normalized as 700 to 750 Joptimum physical properties.

8. A high expansion austenitic steel suitable for use in the manufacture of internal-combustion engines and containing, carbon between 0.35% and 0.97%, manganese from-3L5 to 6%, chromium from 3 to 7%, nickel from!) to 16%, copper from 0.5 to 12%, silicon from 0 to 2.0%, a small proportion of a carbide forming element consisting of vanadium, tungsten, titanium and columbium, the remainder beingsubstantially all iron and the steel having beentnormalized at 700 C. to 750 C. to obtain optimum tensile properties.

,ALFREDEVERETT THORNTON.

REFERENCES CITED The following references are of record in the C. to obtain file of this, patent:

cUll-ITED STATE-SEATENTS Number Name Date 2319;538; Digby F ;May;18; 19 3? FOREIGN PATENTS Number Country Date 695,049 Germany Aug; 14, 1940 and the steel having 

